1. Field of the Invention
This invention relates to a cable connection head for high temperature purposes, which is used to connect a well logging cable and a measuring instrument when lowering various measuring instruments in a well such as a petroleum well and a geothermal well.
2. Description of the Prior Art
In petroleum wells and geothermal wells, well logging is often performed to determine the physical properties of the strata by electrical well logging or acoustic well logging and also determine the properties of the product by flow rate well logging or pressure well logging. For such measurements, it is necessary to lower various measuring instruments (such as well logging sonde) in the well by connecting the instruments to cables. Cable connection heads are used to mechanically and electrically connect the cable and measuring instrument.
The cable connection head consists of three basic elements, i.e., (1) a securement section, to which ends of armoring wires of a well logging cable are secured, (2) a section, in which core wires of the well logging cable are introduced into a head housing, and (3) a connector section, in which the head is connected to the measuring instrument. Of these sections, the section, in which the core wires of the well logging cable are introduced into the head housing, is most important and difficult because it requires water tightness.
A well-known cable head for the purpose noted above has a construction as shown in FIGS. 9 to 11. As is shown, a covered cable 18 is constructed by winding a tape 17 to cover a plurality of covered core wires, each of which consists of a core wire 15 and a polymer cover 14, and a glass fiber 16 intervening between adjacent covered core wires. A well logging cable 19 is constructed by winding a plurality of armoring wires 10 on the outer side of the covered cable 18. The well logging cable 19 is inserted through an upper head housing 3 of a head housing 4, which has a lower head housing 2 coupled to an upper portion of a measuring instrument housing 1 and the upper head housing 3 coupled to an upper portion of the lower head housing 2. The armoring wires 10 of the well logging cable 19 are secured to the upper head housing 3. A plurality of hermetic connectors 20 are secured to the top of the lower head housing 2. Each core wire 15 of the covered cable 18 is connected to one end of each hermetic connector 20. The other end of each hermetic connector 20 is connected by a lead 21 to each terminal of a connector 5 fitted in a lower end portion of a recess 12 of and secured to the lower head housing 2. The connection section between the hermetic connectors 20 and the leads 21 is sealed with a boot 22 made of fluorine-contained rubber in order to prevent intrusion of water into the inside of the hermetic connector 20. Silicone rubber 24 is injected into a connector accommodation chamber 23 in the upper head housing 3 through an injection port 47 to enhance the seal effect. The injection port 47 is then provided with a lid.
The seal property of the above prior art cable connection head at high temperature is determined by the heat resistance of the hermetic connectors 20, fluorine-contained rubber boot 22 and silicone rubber 24. The upper limit of the heat resistance is approximately 270.degree. C., and the head can not be used in high temperature circumstances beyond this temperature. Further, with the prior art cable connection head the minimum diameter is determined by the diameter and number of the hermetic connectors 20. Therefore, it is difficult to manufacture a small diameter cable connection head.